Homogeneous catalyst:
If the catalyst is present in the same phase as the reactants, it is called a homogeneous catalyst and this type of catalyst is called homogeneous catalysis.
Heterogeneous catalyst:
If the catalyst is present in a different phase as the reactants, it is called a heterogeneous catalyst and this type of catalyst is called heterogeneous catalysis.
Types of solids used as catalyst:
Different types of solids are used in heterogeneous catalysis. They may be metals, metal oxides, metal sulphides, clays etc. these materials may be used in their pure form or in the form of their mixtures. Further they may be crystalline, microcrystalline and amorphous. These catalysts are used in a state of file powdered so as to give a large surface area.